The practice of coating implantable medical devices with a synthetic or biological active or inactive agent is known. Numerous processes have been proposed for the application of such a coating. Soaking or dipping the implantable device in a bath of liquid medication is suggested by U.S. Pat. No. 5,922,393 to Jayaraman while soaking in an agitated bath is suggested by U.S. Pat. No. 6,129,658 to Delfino et al. Devices introducing heat and/or ultrasonic energy in conjunction with the medicated bath are disclosed in U.S. Pat. No. 5,891,507 to Jayaraman and U.S. Pat. No. 6,245,4 BI to Alt. U.S. Pat. No. 6,214,1 BI to Taylor et al. suggests spraying the medication by way of pressurized nozzles.
Initially such coatings were applied at the time of manufacture of the medical device. For various reasons, such as the short shelf life of some drugs combined with the time span from manufacture to implantation and the possible decision of the medical staff involved concerning the specific drug and dosage to be used based on the patient's condition at the time of implantation, a need has arisen for technologies which permit applying a coating just prior to implantation. Wrapping the implantable device with medicated conformal film is disclosed in U.S. Pat. No. 6,309,380 BI to Larson et al. Dipping or soaking in a medicated bath just prior to implantation is suggested in U.S. Pat. No. 5,871,436 to Eury, U.S. Pat. No. 6,6,454 to Berg et al., and U.S. Pat. No. 6,1171,232 BI to Papandreou et al. U.S. Pat. No. 6,3,551 BI to Wu provides a bathing chamber for use with specific implantable device such as a stent deployed on the balloon of a catheter.
Each of the methods and devices intended for use just prior to implantation, listed above, deposits the coating material onto any and all surfaces that are exposed to the coating. This may result in depositing coating material on surfaces on which the coating is unwanted or undesirable. Further, the coating may crack or break away when the implantable device is removed from the implantation apparatus. An example of this would be a stent deployed on a catheter balloon. As the balloon is inflated and the stent is expanded into position, the coating may crack along the interface between the stent and the balloon. These cracks may lead to a breaking away of a portion of the coating from the stent itself. Similar problems can occur in cases where the coating technique fails to prevent inadvertent overlapping with the edges, internal surfaces along the edges, of various devices, e.g., struts of stents. This, in turn, may affect the medicinal effectiveness of the coating, and negatively affect the entire medical procedure.
It is known to use ink-jet technology to apply a liquid to selected portion of a surface. In the paper “Applications of Ink-Jet Printing Technology to BioMEMS and Microfluidic Systems,” presented at the SPIC Conference on Microfluidics and BioMEMS, October, 01, the authors, Patrick Cooley, David Wallace, and Bogdan Antohe provide a fairly detailed description of ink-jet technology and the range of its medically (the “Cooley paper”) related applications, http://www.microfab.compapers/papers_pdf/spie biomems_O1_reprint.pdf.
A related device is disclosed in U.S. Pat. No. 6,001,311 to Brennan, which uses a moveable two-dimensional array of nozzles to deposit a plurality of different liquid reagents into receiving chambers. In the Cooley paper and the device of Brennan, the selective application of the material is based on an objective predetermined location for deposit rather that on a “subjective placement” as needed to meet the requirements of a specific application procedure. With regard to the application of coatings applied to medical devices with inkjet applicators, it is possible to coat only a chosen portion of a device, such as only the stent mounted on a catheter, but not the catheter itself. This type of procedure using current technologies may, however, require providing complex data files, such as a CAD image of the device to be coated, and insuring that the device be installed in the coating apparatus in a precise manner so as to be oriented exactly the same as the CAD image.
Other systems which use ink-jet applicators apply the coating with a “freestyle” procedure. The freestyle points are determined by a preprogrammed user selected pattern that is unique to the particular shape or contour for the type of prosthesis and the desired coating to be achieved, much like a vector based printing approach. The ink-jet nozzle or prosthesis move in three-dimensions with the aid of a motion control system. The motion control system enables the ink-jet nozzle to move over the portions of the prosthesis to be sprayed. Alternatively, a real-time picture can be taken with a camera to determine the position of the ink-jet nozzle in relation to the prosthesis. Based upon the feedback of nozzle location, the ink-jet applicator can be controlled by activating the spray, moving the ink-jet nozzle, and/or moving the prosthesis to adjust to the pattern to better conform with the actual prosthesis.
This type of system is particularly inefficient because the preprogrammed user selected pattern fails to accommodate inherent variability in the surface of the prosthesis. In one non-limiting embodiment, for example, a stent crimped around a balloon catheter will not be crimped such that it has the same surface each time. The crimping cannot be determined from the factory according to the manufacturer's specifications of the stent. Further, using this type of feedback loop serves merely as a “first impression” to control the spraying, nozzle position, and/or prosthesis position, and freestyle systems consequently increase the time required to apply the coating. In the operating theatre, this delay is undesired because many types of coatings, e.g., paclitaxel, rapamycin, or several other pharmaceutical compounds or bioactive agents have to be applied to the stent crimped on the balloon catheter immediately prior to surgery.
The significance of delivering drug-loaded prostheses may offer savings benefit in time and cost. Studies have been conducted to show the importance of delivering the correct drug dose density on coronary stents to prevent restenosis by application of paclitaxel or rapamycin. Kandazari, David E. et al., Highlights from American Heart Association Annual Scientific Sessions 2001: Nov. 11 to 14, 2001, American Heart Journal 143 (2), 217-228, 2002; Hiatt, Bonnie L. et al., Drug-Eluting Stents for Prevention of Restenosis: In Quest for the Holy Grail, Catheterization and Cardiovascular Interventions 55:409-417, 2002; Kalinowski, M. et al., Paclitaxel Inhibits Proliferation Of Cell Lines Responsible For Metal Stent Obstruction: Possible Topical Application In Malignant Bile Duct Obstructions, Investigational Radiology 37(7):399-404, 2002. Other studies have shown how accuracy of dose related to cytotoxicity of coating drugs. Liebmann, J. E. et al., Cytotoxic Studies Of Paclitaxel (Taxol) In Human Tumor Cell Lines, Br. J. Cancer, 68(6):1104-9, 1993; Adler, L. M. et al., Analysis Of Exposure Times And Dose Escalation Of Paclitaxel In Ovarian Cancer Cell Lines, Cancer, 74(7):1891-8, 1994; Regar, E. et al., Stent Development And Local Drug Delivery, Br. Med. Bulletin, 59:227-48, 2001. See also http://www.tctmd.com/expert-presentations: Farb, A., Comparative Pathology Of Drug Eluting Stents: Insights Into Effectiveness And Toxicity From Animal Lab, CRF Drug-Eluting Stent Symposium 2002; Grube, E., Taxol-Eluting Stent Trials, ISET 2002 Miami Beach, Mar. 19-23, 2002 (The effect of taxol on the edges of the stent and dose response screening); Carter, Andrew J., Sirolimus: Pre-Clinical Studies—Evaluation Of Dosing, Efficacy And Toxicity, TCT September 2001.